Progressive Progressive Web Apps, Part 1

I like Progressive Web Apps. I like the model it offers for how you build good, solid, reliable websites and apps. I like the principle platform API – service worker – that enables the PWA model to work.
One of the traps that we have fallen into is “App Shell." The App Shell model says that your site should present a complete shell of your application (so that you van experience something even when you are offline) and you then control how and when to pull in content.